Organic EL display device

ABSTRACT

An organic EL display device according to an embodiment of the present invention includes: a substrate; a plurality of pixels located on the substrate; lower electrodes respectively included in the plurality of pixels; a bank defining the plurality of pixels and located between the lower electrodes next to each other; an organic material layer disposed on the lower electrodes and on the bank; and an upper electrode disposed on the organic material layer. A carrier movement preventing layer preventing movement of carriers from the upper electrode to the organic material layer is formed between the organic material layer and the upper electrode on the bank.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Application JP2018-41768 filed on Mar. 8, 2018, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to an organic EL display device.

2. Description of the Related Art

An organic electroluminescent (EL) display device includes a displaypanel in which thin film transistors (TFTs), organic light emittingdiodes (OLEDs), and the like are formed on a substrate. The OLEDincludes an organic material layer between a pair of electrodes. Theorganic material layer is configured by, for example, stacking a holetransport layer, a light emitting layer, an electron transport layer,and the like. The organic material layer is typically formed in a regionsurrounded by a convex bank previously provided to define pixels. Forexample, in JP 2009-88320 A, the organic material layer is formed(separately applied) for each of the pixels; however, when a higherdefinition is achieved or when the aperture ratio of the bank isincreased to enhance luminous efficiency, there is a problem in that itis difficult to control separate applying. On the other hand, forexample when a conductive material of the hole transport layer or thelike is provided common to a plurality of pixels, there is a problem inthat a leakage current flows between the pixels next to each other.Specifically, there is a problem in that the next pixel that should notoriginally emit light emits light due to the leakage current, and thusthat color purity is reduced or image quality is deteriorated. Theproblem may remarkably occur as the definition becomes higher or a drivevoltage becomes lower (e.g., a high-mobility material is employed).

To deal with the above described problem, for example JP 2016-103395 Aproposes to form a divided region in the organic material layer on thebank to prevent the movement of carriers between the pixels next to eachother.

SUMMARY OF THE INVENTION

It is considered that the leakage current not only causes the next pixelto emit light but also causes, for example, light emission on the bank.

In view of the above, it is an object of one or more embodiments of theinvention to provide an organic EL display device in which a troublecaused by a leakage current is suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

An organic EL display device according to an embodiment of the presentinvention includes: a substrate; a plurality of pixels located on thesubstrate; lower electrodes respectively included in the plurality ofpixels; a bank defining the plurality of pixels and located between thelower electrodes next to each other; an organic material layer disposedon the lower electrodes and on the bank; and an upper electrode disposedon the organic material layer. A carrier movement preventing layerpreventing movement of carriers from the upper electrode to the organicmaterial layer is formed between the organic material layer and theupper electrode on the bank.

FIG. 1 is a schematic view showing a schematic configuration of anorganic EL display device according to an embodiment of the invention.

FIG. 2 is a schematic plan view showing an example of a display panel ofthe organic EL display device shown in FIG. 1.

FIG. 3 is a diagram showing an example of a cross section taken alongline in FIG. 2.

FIG. 4 is an enlarged cross-sectional view of an example of the vicinityof a bank of the display panel shown in FIG. 3.

FIG. 5A is a diagram for explaining the positional relationship betweenthe bank and a carrier movement preventing layer.

FIG. 5B is a diagram for explaining the positional relationship betweenthe bank and the carrier movement preventing layer.

FIG. 5C is a diagram for explaining the positional relationship betweenthe bank and the carrier movement preventing layer.

FIG. 5D is a diagram for explaining the positional relationship betweenthe bank and the carrier movement preventing layer.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the invention will be described withreference to the drawings. The disclosure is merely an example.Appropriate modifications that will readily occur to those skilled inthe art and fall within the spirit of the invention are of courseincluded in the scope of the invention. In the drawings, for moreclarity of description, the width, thickness, shape, and the like ofeach part may be schematically represented, compared to those inpracticing aspects of the invention. However, they are merely examplesand do not limit the interpretation of the invention. Moreover, in thespecification and the drawings, elements similar to those described inrelation to a previous drawing are denoted by the same referencenumerals and signs, and a detailed description may be appropriatelyomitted.

Further, in the detailed description of the invention, the terms “on”and “below” as used in defining the positional relationship between onecomponent and another component include, not only the case where onecomponent is located directly on or directly below another component,but also the case where still another component intervenes between thecomponents unless otherwise noted.

FIG. 1 is a schematic view showing a schematic configuration of anorganic EL display device according to an embodiment of the invention.An organic EL display device 2 includes a pixel array section 4 thatdisplays an image, and a drive section that drives the pixel arraysection 4. The organic EL display device 2 includes a display panelconfigured by stacking structures such as TFTs and OLEDs on a substrate.The schematic view shown in FIG. 1 is an example, and the embodiment isnot limited to this configuration.

In the pixel array section 4, OLEDs 6 and pixel circuits 8 are disposedin a matrix corresponding to pixels. The pixel circuit 8 is configuredof a plurality of TFTs 10 and 12 and a capacitor 14.

The drive section includes a scanning line drive circuit 20, a videoline drive circuit 22, a drive power supply circuit 24, and a controller26. The drive section drives the pixel circuit 8 to control lightemission of the OLED 6.

The scanning line drive circuit 20 is connected to scanning signal lines28 each provided for an array of pixels in the horizontal direction (apixel row). The scanning line drive circuit 20 sequentially selects thescanning signal line 28 in response to a timing signal input from thecontroller 26, and applies a voltage for turning on the lighting TFT 10to the selected scanning signal line 28.

The video line drive circuit 22 is connected to video signal lines 30each provided for an array of pixels in the vertical direction (a pixelcolumn). The video line drive circuit 22 receives a video signal fromthe controller 26, and outputs, in synchronization with the selection ofthe scanning signal line 28 by the scanning line drive circuit 20, avoltage in response to the video signal of the selected pixel row toeach of the video signal lines 30. The voltage is written to thecapacitor 14 via the lighting TFT 10 in the selected pixel row. Thedrive TFT 12 supplies a current in response to the written voltage tothe OLED 6, and thus the OLED 6 of the pixel corresponding to theselected scanning signal line 28 emits light.

The drive power supply circuit 24 is connected to drive power supplylines 32 each provided for the pixel column, and supplies a current tothe OLED 6 via the drive power supply line 32 and the drive TFT 12 inthe selected pixel row.

Here, a lower electrode of the OLED 6 is connected to the drive TFT 12.On the other hand, upper electrodes of the OLEDs 6 are configured of anelectrode common to the OLEDs 6 of all pixels. When the lower electrodeis configured as an anode, a high potential is input thereto and a lowpotential is input to the upper electrode that serves as a cathode. Whenthe lower electrode is configured as a cathode, a low potential is inputthereto and a high potential is input to the upper electrode that servesas an anode.

FIG. 2 is a schematic plan view showing an example of the display panelof the organic EL display device shown in FIG. 1. In a display region 42of a display panel 40, the pixel array section 4 shown in FIG. 1 isprovided, and the OLEDs 6 are arranged in the pixel array section 4 asdescribed above. The upper electrode constituting the OLED 6 is formedcommon to the pixels as described above, and covers the entire displayregion 42.

On one side of the display panel 40 having a rectangular shape, acomponent mounting region 46 is provided. Wiring lines connected to thedisplay region 42 are disposed on the component mounting region 46. Adriver integrated circuit (IC) 48 constituting the drive section ismounted in the component mounting region 46, and a flexible printedcircuit (FPC) 50 is connected thereto. The FPC 50 is connected to thecontroller 26, the circuits 20, 22, and 24, and the like, and an IC ismounted on the FPC 50.

FIG. 3 is a diagram showing an example of a cross section taken alongline in FIG. 2. The display panel 40 has a structure in which a circuitlayer 74 including TFTs 72, the OLEDs 6, a sealing layer 106 sealing theOLEDs 6, and the like are stacked on a substrate 70. The substrate 70 isconfigured of, for example, a glass plate or a resin film (e.g., a resinfilm containing resin such as polyimide-based resin). In the embodiment,the pixel array section 4 is of a top-emission type, and light generatedby the OLED 6 is emitted to the side (upward in FIG. 3) opposite to thesubstrate 70 side.

In the circuit layer 74 of the display region 42, the pixel circuit 8,the scanning signal line 28, the video signal line 30, the drive powersupply line 32, and the like, which are described above, are formed. Atleast a portion of the drive section can be formed as the circuit layer74 in a region next to the display region 42 on the substrate 70. Asdescribed above, the driver IC 48 which constitutes the drive sectionand the FPC 50 can be connected to a wiring line 116 of the circuitlayer 74 in the component mounting region 46.

As shown in FIG. 3, an under layer 80 formed of an inorganic insulatingmaterial is disposed on the substrate 70. As the inorganic insulatingmaterial, for example silicon nitride (SiN_(y)), silicon oxide(SiO_(x)), or a complex of these materials is used.

In the display region 42, a semiconductor region 82 serving as a channelportion and a source-drain portion of the TFT 72 of a top-gate type isformed on the substrate 70 via the under layer 80. The semiconductorregion 82 is formed of, for example, polysilicon (p-Si). Thesemiconductor region 82 is formed by, for example, providing asemiconductor layer (p-Si film) on the substrate 70, and patterning thesemiconductor layer to selectively leave portions to be used for thecircuit layer 74.

Above the channel portion of the TFT 72, a gate electrode 86 is disposedvia a gate insulating film 84. The gate insulating film 84 is typicallyformed of TEOS. The gate electrode 86 is formed by, for example,patterning a metal film formed by sputtering or the like. An interlayerinsulating layer 88 is disposed so as to cover the gate electrode 86 onthe gate electrode 86. The interlayer insulating layer 88 is formed of,for example, the inorganic insulating material described above. Animpurity is introduced by ion implantation into the semiconductor region82 (p-Si) serving as the source-drain portion of the TFT 72, andfurther, a source electrode 90 a and a drain electrode 90 b that areelectrically connected to the semiconductor region 82 are formed, sothat the TFT 72 is configured.

An interlayer insulating film 92 is disposed on the TFT 72. A wiringline 94 is disposed on the surface of the interlayer insulating film 92.The wiring line 94 is formed by, for example, patterning a metal filmformed by sputtering or the like. Using the metal film forming thewiring line 94 and the metal film used for the formation of the gateelectrode 86, the source electrode 90 a, and the drain electrode 90 b,for example, the scanning signal line 28, the video signal line 30, andthe drive power supply line 32, which are shown in FIG. 1, and thewiring line 116 can be formed to have a multilayer wiring structure. Aplanarization film 96 and a passivation film 98 are formed on thisstructure, and the OLED 6 is formed on the passivation film 98 in thedisplay region 42. The planarization film is formed of, for example, aresin material. The passivation film 98 is formed of, for example, aninorganic insulating material such as SiN_(y).

The OLED 6 includes a lower electrode 100, an organic material layer102, and an upper electrode 104. The OLED 6 is typically formed bystacking the lower electrode 100, the organic material layer 102, andthe upper electrode 104 in this order from the substrate 70 side. In theembodiment, the lower electrode 100 is an anode of the OLED 6, and theupper electrode 104 is a cathode thereof.

When it is assumed that the TFT 72 shown in FIG. 3 is a drive TFT 12having an n-channel, the lower electrode 100 is connected to the sourceelectrode 90 a of the TFT 72. Specifically, after the formation of theplanarization film 96 described above, a contact hole 110 for connectingthe lower electrode 100 to the TFT 72 is formed, and by, for example,patterning a conductor portion formed on the surface of theplanarization film 96 and within the contact hole 110, the lowerelectrode 100 connected to the TFT 72 is formed for each pixel. Thelower electrode 100 is formed of, for example, transparent metal oxidesuch as indium tin oxide (ITO) and indium zinc oxide (IZO), or metalsuch as Ag and Al.

A bank 112 separating pixels is disposed on the structure describedabove. The bank 112 is used to electrically separate the lowerelectrodes 100 provided corresponding to the respective pixels, and isformed so as to cover the peripheral edge of the lower electrode 100from the upper surface to the side surface. Specifically, the bank 112includes an opening exposing a portion of the lower electrode 100. Thebank 112 is typically formed of a resin material such as polyimide-basedresin and acrylic-based resin. The side surface of the bank 112 includesan inclined surface that is inclined toward the substrate 70 side as itis extended toward the lower electrode 100 side (outside).

For example, after the formation of the lower electrode 100, the bank112 is formed at a pixel boundary, and the organic material layer 102and the upper electrode 104 are stacked in an effective region (a regionwhere the lower electrode 100 is exposed) of a pixel surrounded by thebank 112. The organic material layer 102 (in some cases, light emittinglayers 102 b to be described later may be excluded) and the upperelectrode 104 are provided common to pixels, and are provided not onlyon the upper surface of the lower electrode 100 but also on the bank112.

The organic material layer 102 typically includes a plurality of layers.Specifically, the organic material layer 102 is formed by stacking ahole transport layer, a light emitting layer, and an electron transportlayer in order from the anode side. Moreover, the organic material layer102 may include another layer. Examples of another layer include, forexample, a hole injection layer or electron blocking layer disposedbetween the anode and the light emitting layer and an electron injectionlayer or hole blocking layer disposed between the cathode and the lightemitting layer. The upper electrode 104 is configured of a transmissiveconductive film. The transmissive conductive film is formed of, forexample, an extremely thin alloy of Mg and Ag, or a transparent metaloxide such as ITO and IZO.

A sealing layer 106 is disposed on the upper electrode 104. The sealinglayer 106 may function, for example, as a protective layer to protectthe OLED 6 from moisture and the like, and therefore is formed so as tocover the entire display region 42. The sealing layer 106 is formed by,for example, depositing an inorganic insulating material film of SiN_(y)or the like by a chemical vapor deposition (CVD) method. Although notshown in the drawing, for example a protective film is disposed on thesurface of the display region 42 for ensuring the mechanical strength ofthe surface of the display panel 40. Specifically, a sheet-like orfilm-like protective film is bonded on the sealing layer 106 via anadhesion layer. In this case, the protective film is not generallyprovided in the component mounting region 46 for facilitating theconnection of the IC or the FPC. A wiring line of the FPC 50 and aterminal of the driver IC 48 are electrically connected to, for example,the wiring line 116.

A carrier movement preventing layer 108 is formed between the organicmaterial layer 102 and the upper electrode 104 on the bank 112. Thecarrier movement preventing layer 108 is in direct contact with theorganic material layer 102 and the upper electrode 104. Disposing thecarrier movement preventing layer 108 between the organic material layer102 and the upper electrode 104 suppresses the injection of carriersfrom the upper electrode 104 into the organic material layer 102 on thebank 112, which may prevent light emission on the bank 112 and thuscontribute to an improvement in luminous efficiency and an improvementin display characteristics (e.g., front chromaticity and visualcharacteristics).

FIG. 4 is an enlarged cross-sectional view of an example of the vicinityof the bank of the display panel shown in FIG. 3, in which, in thestacked structure of the display panel 40 shown in FIG. 3, a stackedstructure from the under layer 80 to the passivation film 98 on thesubstrate 70 is shown in a simplified manner as an upper structure layer114, and the sealing layer 106 is omitted. The organic material layer102 is formed, for example, as follows: a hole transport layer 102 a iscontinuously formed (provided common to a plurality of pixels) on thelower electrode (anode) 100 and the bank 112; the light emitting layers102 b corresponding to the colors of the respective pixels are formed inrespective pixel regions on the hole transport layer 102 a; and anelectron transport layer 102 c is formed so as to cover the lightemitting layers 102 b (common to the plurality of pixels). The lightemission on the bank 112 may occur when the light emitting layer 102 bis present on the bank 112 as shown in FIG. 4. Specifically, when holesare injected from the anode 100 into the organic material layer 102while electrons are injected from the cathode 104 into the organicmaterial layer 102, the holes and the electrons are recombined togetherin the light emitting layer 102 b and thus the light emitting layer 102b emits light. However, when the light emitting layer 102 b is presenton the bank 112, light emission may also occur on the bank 112. Thelight emission on the bank 112 is relatively weak (e.g., light emissionto such an extent that can be confirmed by microscopic observation or ata level that is not confirmed by microscopic observation but can beconfirmed by microspectroscopy) but may affect luminous efficiency ordisplay characteristics. As described above, disposing the carriermovement preventing layer 108 between the organic material layer 102 andthe upper electrode 104 on the bank 112 suppresses the injection ofcarriers (electrons) from the upper electrode (cathode) 104 into theorganic material layer 102, which may prevent light emission on the bank112.

The carrier movement preventing layer 108 is formed of any appropriatematerial that may prevent the movement of carriers from the upperelectrode 104 to the organic material layer 102. In one embodiment, theconfiguration of the carrier movement preventing layer 108 is determineddepending on the upper electrode 104. For example, when the upperelectrode 104 is a cathode as described above, the carrier movementpreventing layer 108 is formed of a material that may prevent themovement of electrons from the upper electrode 104 to the organicmaterial layer 102. For example, the carrier movement preventing layer108 is formed of a material that forms a layer having an electronmobility lower than that of an electron injection layer or electrontransport layer that may be included in the organic material layer 102.Specific examples of the layer include a hole transport layer that mayconstitute the organic material layer 102. In this case, the carriermovement preventing layer 108 can be formed of a material that forms theorganic material layer 102, which may be excellent in manufacturingefficiency. Examples of the material forming the hole transport layerinclude 4,4′-bis[N-(naphthyl)-N-phenyl-amino]biphenyl (α-NPD),N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TPD), 2-TNATA,and 4,4′,4″-tris(N-(3-methylphenyl)N-phenylamino)triphenylamine(MTDATA). In another embodiment, the carrier movement preventing layer108 is formed of an insulating material. That is, the carrier movementpreventing layer 108 may be an insulating layer. As the insulatingmaterial, for example, an inorganic insulating material represented bysilicon nitride (SiN_(y)), silicon oxide (SiO_(x)), and a complex ofthese materials, resin, or the like is used.

The carrier movement preventing layer 108 may be formed by anyappropriate method. Examples of the forming method include, for example,deposition by mask evaporation using a mask having a pattern, anddeposition by a laser transfer method. The thickness of the carriermovement preventing layer 108 is, for example, from 5 nm to 50 nm.

FIGS. 5A to 5D are diagrams for explaining the positional relationshipbetween the bank and the carrier movement preventing layer. In apreferred embodiment, as shown in FIG. 5A, the carrier movementpreventing layer 108 is formed such that the carrier movement preventinglayer 108 covers the entire bank 112 and does not overlap the opening ofthe bank 112 with an edge portion of the carrier movement preventinglayer 108 aligned with an edge portion of the bank 112. In anotherembodiment, as shown in FIG. 5B, the carrier movement preventing layer108 is formed so as to cover at least an edge portion (inclined surface)112 a of the bank 112, and is opposed to the edge portion of the bank112. In addition, the carrier movement preventing layer 108 is notformed at a central portion 112 b of the bank 112. It can be said thatthe central portion 112 b of the bank 112 is a central portion of theupper surface of the bank 112 located between the lower electrodes 100next to each other. Light emission on the bank 112 is stronger as theplace is closer to the opening of the bank 112, and in this embodiment,the carrier movement preventing layer 108 is selectively formed at aplace where light emission is strong. In still another embodiment, asshown in FIG. 5C, the carrier movement preventing layer 108 is formed atat least the central portion 112 b of the bank 112 so as to cover thecentral portion 112 b, and is not formed at the edge portion (inclinedsurface) 112 a of the bank 112. This embodiment is preferable in termsof, for example, low difficulty of formation of the carrier movementpreventing layer 108. In still further another embodiment, as shown inFIG. 5D, the carrier movement preventing layer 108 is formed such thatthe carrier movement preventing layer 108 covers the entire bank 112,and that an edge portion of the carrier movement preventing layer 108also covers the opening of the bank 112. In this embodiment, an openingregion (light emitting region) of the bank 112 is small; however, lightemission on the bank 112 may be effectively prevented.

The invention is not limited to the embodiments, and variousmodifications can be made. For example, the configuration described ineach of the embodiments may be replaced with substantially the sameconfiguration, a configuration providing the same operational effect, ora configuration capable of achieving the same object.

Various altered and modified examples within the idea of the inventionwill occur to those skilled in the art, and it is understood that thealtered and modified examples also belong to the scope of the invention.For example, when those skilled in the art appropriately add or remove acomponent or change the design of a component in the embodimentsdescribed above, or add or omit a step or change the conditions of astep in the embodiments described above, the modification is alsoincluded in the scope of the invention as long as they include thespirit of the invention.

What is claimed is:
 1. An organic EL display device comprising: asubstrate; a plurality of pixels located on the substrate; lowerelectrodes respectively included in the plurality of pixels; a bankdefining the plurality of pixels and located between the lowerelectrodes next to each other; an organic material layer disposed on thelower electrodes and on the bank; and an upper electrode disposed on theorganic material layer, wherein a carrier movement preventing layerpreventing movement of carriers from the upper electrode to the organicmaterial layer is formed between the organic material layer and theupper electrode directly above the bank, wherein the upper electrode isa cathode, and the carrier movement preventing layer contains a materialcontained in a hole transport layer constituting the organic materiallayer.
 2. The organic EL display device according to claim 1, whereinthe carrier movement preventing layer is in direct contact with theorganic material layer and the upper electrode.
 3. The organic ELdisplay device according to claim 1, wherein the organic material layerincludes a plurality of layers, and at least a portion of the layers ofthe organic material layer extends over the plurality of pixels.
 4. Theorganic EL display device according to claim 1, wherein the upperelectrode is a cathode, and the carrier movement preventing layer is alayer having an electron mobility lower than that of an electroninjection layer or electron transport layer constituting the organicmaterial layer.
 5. The organic EL display device according to claim 1,wherein the upper electrode is a cathode, and the carrier movementpreventing layer contains one or more kinds selected from the groupconsisting of 4,4′-bis[N-(naphthyl)-N-phenyl-amino]biphenyl (α-NPD),N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TPD), 2-TNATA,and 4,4′,4″-tris(N-(3-methylphenyl)N-phenylamino)triphenylamine(MTDATA).
 6. The organic EL display device according to claim 1, whereinthe carrier movement preventing layer contains an insulating material.7. The organic EL display device according to claim 1, wherein an edgeportion of the bank and an edge portion of the carrier movementpreventing layer overlap in a plan view.
 8. The organic EL displaydevice according to claim 1, wherein the carrier movement preventinglayer is opposed to at least an edge portion of the bank.
 9. The organicEL display device according to claim 1, wherein the bank includes anupper surface located between the lower electrodes next to each other,and the carrier movement preventing layer is opposed to at least acentral portion of the upper surface.
 10. The organic EL display deviceaccording to claim 1, wherein the bank includes an opening exposing aportion of the lower electrode, the carrier movement preventing layercovers the bank, and an edge portion of the carrier movement preventinglayer is opposed to a portion of the opening.